Optical receiver comprising a receiver photodetector integrated with an imaging array

Abstract

A high-speed optical communications cell is integrated at the interior of a two-dimensional imaging array. The combined receiver and imager carries out both photodetection (converting photons to electrons) and circuit functions (e.g. amplifying and integrating the signals from the photodetectors). The high-speed receiver cell comprises a photodetector and a high-speed amplification circuit, providing an electrical output which can follow a rapidly varying optical signal falling on the photodetector. The imaging array comprises an array of photodetectors and readout circuits, providing an electrical representation of the variation of light with position across the receiver surface. The presence of an imaging array surrounding the communications receiver, and in the same plane as it, allows a single optical path to be used for source acquisition and tracking as well as for data reception.

1. An apparatus comprising:
 a substrate comprising a first photosensitive crystalline semiconductor material; and 
 a plurality of photodetectors integrated on the substrate, the plurality of photodetectors comprising:
 at least one first photodetector comprising the first photosensitive crystalline semiconductor material; and 
 at least one second photodetector comprising a second photosensitive crystalline semiconductor material chemically different from the first photosensitive crystalline semiconductor material, 
 
 wherein the at least one second photodetector is configured as at least part of an optical receiver cell, integrated on the substrate, to receive an optical signal beam from a signal source and to convert the optical signal beam to an electrical signal; and 
 wherein a subset of the plurality of photodetectors is configured as an optical imaging array, 
 wherein the optical imaging array comprises a plurality of imaging cells to image the signal source for aligning the optical receiver cell with the signal source, wherein the plurality of imaging cells comprises at least 100 imaging cells, and wherein at least one imaging cell of the plurality of imaging cells comprises the at least one first photodetector. 
 
     
     
       2. The apparatus of  claim 1  wherein the optical receiver cell is a high speed cell configured to follow a variation of the optical signal beam. 
     
     
       3. The apparatus of  claim 2 ,
 wherein the optical receiver cell is a high speed cell with a response speed of at least 10 megahertz; and 
 wherein at least sixteen imaging cells of the plurality of imagine cells have a response speed of less than 500 kilohertz. 
 
     
     
       4. The apparatus of  claim 3  wherein the optical receiver cell has a response speed of one gigahertz or more and each of the at least sixteen imaging cells of the plurality of imaging cells has a response speed of 30 hertz or less. 
     
     
       5. The apparatus of  claim 3  wherein each imaging cell of the plurality of imaging cells comprises a respective photodetector, and the respective photodetectors of the plurality of imaging cells are coplanar to within 10 micrometers or less. 
     
     
       6. The apparatus of  claim 1  wherein the optical receiver cell is a high speed cell that further comprises a high speed amplifier coupled to the at least one second photodetector. 
     
     
       7. The apparatus of  claim 1  wherein the substrate comprises silicon, and the plurality of imaging cells comprise silicon readout circuits to provide an electrical representation of a variation of light with position across a surface of the optical imaging array. 
     
     
       8. The apparatus of  claim 1  wherein the plurality of imaging cells are disposed about the optical receiver cell and are substantially co-planar with the optical receiver cell. 
     
     
       9. The apparatus of  claim 1  wherein the optical receiver cell and the plurality of imaging cells receive light from the signal source in a single optical path. 
     
     
       10. The apparatus of  claim 1  further comprising a positioning mechanism and a tacking control circuit, the tracking control circuit responsive to at least one electrical output from the plurality of imaging cells to generate a tracking signal for directing the positioning mechanism to maintain accurate pointing of the optical receiver cell toward the signal source. 
     
     
       11. The apparatus of  claim 1  wherein each imaging cell of the plurality of imaging cells comprises an integrating circuit to accumulate electrical energy from illumination over a period of time. 
     
     
       12. A line of sight optical communication system comprising:
 the signal source for transmitting the optical signal beam through atmosphere or space, and 
 an optical receiver system for receiving the transmitted beam, the optical receiver system comprising collection optics for collecting and concentrating the transmitted beam to form a concentrated beam, a variable focal length lens for collimating the concentrated beam to form a collimated beam or converging the concentrated beam to form a converged beam, and an apparatus according to  claim 1 . 
 
     
     
       13. The communication system of  claim 12  wherein the collimated beam is distributed over substantially all of the imaging cells of the plurality of imaging cells and the converged beam is concentrated essentially on the optical receiver cell. 
     
     
       14. The communication system of  claim 12  wherein an amount of power incident on imaging cells of the plurality of imaging cells adjacent the optical receiver cell is monitored to detect deviation of the optical signal beam from the optical receiver cell. 
     
     
       15. The apparatus of  claim 1  wherein the first photosensitive crystalline semiconductor material is silicon and the second photosensitive crystalline semiconductor material is selected from the group consisting of germanium, germanium alloy, InGaAs and HgCdTe. 
     
     
       16. The apparatus of  claim 1  wherein the second photosensitive crystalline semiconductor material is epitaxially grown on the first photosensitive crystalline semiconductor material. 
     
     
       17. The apparatus of  claim 1  wherein the first photosensitive crystalline semiconductor material is crystalline silicon and the second photosensitive crystalline semiconductor material is epitaxially grown on the silicon. 
     
     
       18. The apparatus of  claim 17  wherein the second photosensitive crystalline semiconductor material comprises germanium. 
     
     
       19. The apparatus of  claim 1 , wherein the plurality imaging cells comprises at least one hundred thousand imaging cells.